Characterization of iron oxide-dispersed activated carbon fibres with Fe K-edge XANES and EXAFS and with water adsorption

Abstract

The Fe K-edge X-ray absorbtion near-edge structure (XANES) and extended X-ray absorption fine structure (EXAFS) and the water adsorptivity of iron oxide-dispersed activated carbon fibres (ACF) have been investigated. Also, Fe K-edge XANES and EXAFS of various kinds of powdered iron oxides have been measured in order to characterize the species disperesed on the ACF. The XANES and EXAFS indicated that α-FeOOH-like ultrafine particles transform into α-Fe₂O₃-like particles on the ACF through heating in vacuo. The adsorption isotherms of water on the α-FeOOH-dispersed ACF were of type V. The water adsorption isotherms were analysed by the Dubinin–Serpinsky equation; the number of polar sites on the surface was estimated and compared with the data from an analysis of the evolved gas. The relationship between the water adsorptivity and the states of the iron oxides on the ACF is discussed. A comparison of nitrogen and water adsorption shows that the layer of water adsorbed on iron oxides dispersed on the ACF has a more sparse structure than normal water, and that the iron oxide-dispersed and preoxidized ACF samples exhibit an excess of water adsorptivity owing to both molecular-sieve effects and surface fractal structure.